1. Field of the Invention
This invention relates to a surface inspecting apparatus, and more particularly, to a flying spot type surface inspecting apparatus which inspects defects existing on a suface of a subject matter to be inspected such as a film, a paper, iron or the like by using a light beam.
2. Description of the Related Art
A conventional flying spot type surface inspecting apparatus comprises a scanner which includes a laser beam source irradiating a light beam, a lens system, a rotating mirror and the like, a light receiver receiving transmitted light or reflected light from the subject matter being inspected, and a processing circuit which discriminates the presence of a defect by making use of photoelectric conversion signals obtained from the light receiver. FIG. 1 shows an example of the surface inspecting apparatus above-mentioned.
In FIG. 1, a scanning light beam 11, which is irradiated from a scanner 10, traces a scanning line 12a on the surface of a subject matter 12 moving in an X-direction. After being reflected on the surface of the subject matter 12 in the position of the scanning line 12a, the light beam 11 enters a light detector 13 to be photoelectrically converted. The electric signal outputted from the light detector 13 is subjected to the waveform shaping in a filtering circuit 14 so as to intensify a portion having a defect. The signals are classified by a threshold level in a binarizing circuit 16 into two classifications. For example, the signal over a threshold level is allotted to "1" as a defect signal and the signal under a threshold level is allotted to "0" as a normal signal.
On the other hand, a photosensor 17 installed together with the scanner 10 receives the initial light beam 11 of every scanning and electrically converts the received light beam 11 into an electric signal to be outputted. When the electric signal is given, a counter 18 starts to count a number of reference pulses having a sufficiently-short and a constant cycle formed in a reference pulse generator 19. A comparing circuit 22 outputs "0" until the counting number increases from zero to a predetermined value (which corresponds to a starting position K.sub.1 preset by means of a starting position preset circuit 21) while another comparing circuit 23 outputs "1". When the counting number exceeds the predetermined value corresponding to the starting position K.sub.1 which is set in advance, the comparing circuit 22 changes its value from "0" to "1" and maintains the new value. By this, an AND circuit 24 continues outputting "1". Sequentially, when the counting number of the reference pulse gets over another predetermined value which corresponds to an ending position K.sub.2 preset by means of an ending position preset circuit 26, the comparing circuit 23 changes its output value from "1" to "0". Thereafter, the AND circuit 24 maintain the new value "0".
As described above, an inspecting width gate circuit 27 which is enclosed with a broken line outputs an inspecting width gate signal E as shown in FIG. 2E. Therefore, only when the aforementioned binarizing circuit 16 outputs a defect signal "1", all of the signals to be inputted into the AND circuit 27 become "1", and thereby the AND circuit 27 is to output a digital signal "1" which corresponds to a defect detecting signal F as shown in FIG. 2F.
FIGS. 2A to 2F show waveforms of the signals A to F corresponding to their respective portions in the processing circuit shown in FIG. 1. In these figures, when an effective inspecting range in the direction of the scanning is defined narrower than the width of the subject matter 12 by determining the values K.sub.1 and K.sub.2 to be preset, it is possible to continuously inspect the subject matter 12 skipping the edge portions thereof. This enables the defect detecting signal F to be detected separately from the noise made by the edges of the subject matter 12 shown in FIG. 2C.
In the conventional surface inspecting apparatus described above, the starting point and the ending point of the effective inspection need be manually set up by means of switches or the like so that the counter 18 may count up the reference clock in order to define the gate signal between the start setting point K.sub.1 and the end setting point K.sub.2. Therefore, the conventional method has a disadvantage in that the set-up for the starting point and the ending point must be changed whenever the width of the subject matter changes.